U.S. Pat. No. 7,245,789 to Bates et al. (hereafter “Bates”), titled “Systems and Methods for Minimally-Invasive Optical-Acoustic Imaging,” which issued on Jul. 17, 2007, discusses a device well suited to the unique and demanding application of cardio-vascular Imaging and also potential applications within the field of neuro-vascular imaging, among others. Bates describes a device that may include a combination of a resonant cavity within an optical fiber that acts as an ultrasound receiver, and a method for creating an ultrasound wave within the cavity for the ultrasound generator or transmit function. These functions are realized by the use of Fiber Bragg Gratings (FBGs).
The imaging guidewire in Bates may have a diameter similar to that of standard guidewires. As such, the imaging guidewire in Bates may be compatible with many existing therapies. The small diameter of the imaging guidewire in Bates may mean that it can remain in place while therapies are administered, and that it can be used to provide feedback without the need for “Catheter Exchange.” Catheter exchange may be necessary for other imaging devices as the existing imaging catheters may be too large to be deployed along with a therapy. Catheter exchange may lead to an undesirable situation in which the clinician needs to exchange or swap imaging and therapy catheters several times during a procedure before the therapy has been judged as being successful. As such, catheter exchange may be time consuming and, in some cases, traumatic for the patient. With the Bates design, it is possible to both administer a therapy and have the imaging guidewire in place simultaneously, which can drastically reduce the time for a procedure and lead to a much better application of the therapy and patient outcomes by real-time monitoring.
The Bates device may image a cross-sectional slice of a vessel inside which it is inserted. The image may be referred to as a two-dimensional (“2D”) image because at any given time it is imaging a single slice of the vessel. The image thickness of the single slice may be on the order of several hundred microns (0.000001 meter) to one millimeter (“mm”) with a resolution that is on the order of tens of microns.
In some example implementations, existing imaging devices may generate a “pseudo” three-dimensional (“3D”) image of the vessel. The pseudo-3D image may be generated over a length of the vessel that may range from a few millimeters to a few centimeters (“cm”) using a technique known as “pull back.” “Pull back” involves slowly retracting the imaging device along the section of the vessel to be imaged, and then using an imaging system to construct a 3D image from the individual slices captured during the pull back.
The “pull back” technique may not be ideal as it may take several minutes to complete and it is often unreliable as the imaging device is moving during the process. This can lead to smearing of the image because of vessel movement, spiral motion of the imaging device, and other effects. A smeared image may lead to loss of important detail and an inaccurate representation of the vessel.
One example technique described in Bates is to scale the imaging to 3D by replicating the sensors multiple times along a desired length of the guidewire. A technique such as Wavelength Division Multiplexing (WDM) may be used to uniquely distinguish each of the slices. In this case, a complete and unique set of optical components and electronics for each of the slices may be necessary. In one example implementation, ten slices of a vessel may require 320 receive lasers, based on 32 imaging elements on the guidewire per slice, and 10 pulsed lasers to implement the transmit function.